This invention relates to a composite barrel and to a process for the manufacture thereof, said barrel being more particularly intended for automatic weapons.
Automatic weapons are mechanisms the sub-assemblies and the constituting parts of which are subjected to severe operating stresses. This is particularly the case for barrels and especially for barrels of weapons used at very high rates of fire such as the barrels of machine-guns. In that case, the metal of the barrel is mechanically stressed while being maintained at a very high temperature and in any case higher than 500.degree. C. This temperature rise results from the combustion of the propelling powder and from friction. The available energy is principally used for moving the projectile, but a substantial fraction of said energy is converted into heat radiating outwardly through the metal of the barrel which strongly warms up. In fact, the involved stresses may be resumed as follows:
the erosion and the corrosion through the combustion gases of the propelling powder; PA1 the thermal fatigue resulting from the repeated mechanical stresses at a high temperature; PA1 the friction resulting from the passage of the projectile which, starting from a zero speed, reaches a speed of several hundreds of m/sec. within one millisecond; PA1 an internal pressure of several thousands of bars inducing, in the barrel, mechanical stresses which are substantial, but of short duration. PA1 a high mechanical strength at room temperature and at 900.degree. C.; PA1 a good resilience down to -60.degree. C.; PA1 a small friction coefficient relative to the materials used as projectile coatings even at temperatures of about 1000.degree. C.; PA1 a substantial resistance to the corrosion caused by the combustion gases of the propelling powders; PA1 a low tendency to the thermal fatigue; PA1 a substantial thermal conductivity; PA1 a good formability by means of conventional equipments allowing the internal rifling and the external machining without major difficulties. PA1 for the internal layer: chromium, tungsten, niobium, tungsten carbide and the like or alloys thereof; PA1 for the core layer: cobalt alloys such as those used for turbo-jets; PA1 for the external layer: alloyed steels, e.g. chromium-molybdenum alloys allowing a relatively easy machining.
These phenomenons are well known by those skilled in the art who tried, through various means, to find solutions to this complex problem. In fact, although the alloyed steels (materials generally used for manufacturing barrels) do allow a perfect operation of the weapons at relatively slow rates of fire, they do not make it possible to obtain high rates of fire for a substantial time interval. Accordingly, the life of a barrel made of steel and used at high rates of fire is relatively short. Thus, it may be said that it is really necessary to provide a barrel allowing high rates of fire with an acceptable useful life under such conditions. In fact, such barrel should have the following characteristics: